The present invention relates to a slab type gas laser, more specifically to a construction to provide an excellent laser beam having substantially Gaussian distribution in focused output laser beam profile.
A slab type gas laser is known as one type of gas lasers such as CO2 (carbon dioxide) laser. In a slab type gas laser, the gap between excitation electrodes is narrow so that the excited gas colliding with the electrodes is cooled, thereby accelerating the release of laser lower level. This is the reason why the laser is known as an electrode diffusion cooling type laser.
The slab type gas laser is classified into a waveguide type gas laser and a straight type gas laser depending on the way how the light propagates. In the waveguide type gas laser including a CO2 laser of 10 μm emission wavelength, the gap between two electrodes is in the order of approximately several m m. The laser beam propagates in the waveguide mode by being reflected between the electrodes in a zigzag manner. On the other hand, in the straight type gas laser, the gap between the electrodes is large enough so that the light can propagate in the free space. As a result, the light propagates between the two electrodes in the free space mode.
A known cylindrical straight slab type gas laser comprises a pair of cylindrical electrodes of different diameter disposed horizontally and concentrically by way of spacers. The gap between the two cylindrical electrodes is filled with laser medium to define a cylindrical straight slab. A ring-shaped trick mirror is disposed at one end of the cylindrical straight slab and an output mirror (half mirror) is disposed at the center of the one end to pass a part of the light and to reflect a part of the remaining light. A w-axicon mirror is disposed at the other end of the cylindrical straight slab.
Also, it is typical in a conventional slab type gas laser employing such cylindrical straight slab to set the center offset of the trick mirror larger than the center position of the mirror itself in order to provide a larger output as described in detail hereinafter.